Composite polyamide membrane post-treated with nitrous acid

ABSTRACT

A method for making a composite polyamide membrane comprising a porous support and a polyamide layer, including the steps of: i) applying a polar solution comprising of polyfunctional amine monomer and a non-polar solution comprising a polyfunctional acyl halide monomer to a surface of a porous support and interfacially polymerizing the monomers to form a polyamide layer; and ii) exposing the thin film polyamide layer to nitrous acid; wherein the method is characterized by at least one of: conducting the interfacial polymerization of step i) in the presence of a subject amine-reactive compound, or applying a subject amine-reactive compound to the interfacially polymerized polyamide layer prior to step ii), wherein the subject amine-reactive compound is different from the polyfunctional acyl halide and polyfunctional amine monomers and is represented by the following formula:

FIELD

The present invention is generally directed toward composite polyamidemembranes along with methods for making and using the same.

INTRODUCTION

Composite polyamide membranes are used in a variety of fluidseparations. One common class of membranes includes a porous supportcoated with a “thin film” polyamide layer. The thin film layer may beformed by an interfacial polycondensation reaction betweenpolyfunctional amine (e.g. m-phenylenediamine) and polyfunctional acylhalide (e.g. trimesoyl chloride) monomers which are sequentially coatedupon the support from immiscible solutions, see for example U.S. Pat.No. 4,277,344 to Cadotte. Various constituents may be added to one orboth of the coating solutions to improve membrane performance. Forexample, U.S. Pat. No. 6,878,278 to Mickols describes the addition of awide range of additives to one or both coating solutions includingvarious tri-hydrocarbyl phosphate compounds. US2013/0287944,US2013/0287945, US2013/0287946, WO2013/048765 and WO2013/103666 describethe addition of various monomers that include both carboxylic acid andamine-reactive functional groups in combination with varioustri-hydrocarbyl phosphate compounds.

U.S. Pat. No. 4,888,116 to Cadotte describes the use of combinations ofbi- and tri-functional acyl halide monomers, e.g. isophthaloyl chlorideor terephthaloyl chloride with trimesoyl chloride. The resultingpolyamide layer is subsequently post-treated with a reagent (nitrousacid) to form diazonium salt groups and corresponding derivatives (e.g.azo linkages) from unreacted pendant amine groups. See alsoWO2013/047398, US2013/0256215, US2013/0126419, US2012/0305473,US2012/0261332 and US2012/0248027. The concentration and location of theazo groups in the membrane are specific to the number of amine endgroups and their distribution along the polymer chains and the relativerates of diazonium salt hydrolysis and azo coupling. As a consequence,the number of possible azo groups is limited and the formation ofinter-chain cross linking only occurs through end groups in between twodifferent polymer chains. Hence this approach limits the number ofpossible azo groups and introduces inter-chain cross linking onlythrough end groups in between two different polymer chains.

In one embodiment, the invention eliminates this restriction andprovides synthetic routes to increase the number of azo groups and alsointroduces intra chain crosslinking through multiple sites on thepolymer backbone. This creates a tighter and more uniform polymernetwork. In another embodiment, the invention eliminates theabove-mentioned restriction and provides synthetic routes to increasethe number of azo groups preferentially distributed near the surface ofthe polymer. In contrast to distributing azo crosslinking uniformlythroughout the whole polymer, this embodiment preferentially “tightensup” the surface and not the bulk of the membrane. As a result, theopenness of the polymer in the bulk is preserved and a gradient ofcrosslinking density from the feed side surface to the polysulfonesupport facing surface is created with the feed side of the membranebeing more crosslinked. This unique structure improves selectivitybetween water and salt transport. Specifically the neutral and largermolecules are more efficiently rejected without sacrificing the flux ofthe membrane.

SUMMARY

The invention includes a method for making a composite polyamidemembrane including a porous support and a thin film polyamide layer. Themethod includes the steps of: i) applying a polar solution comprising apolyfunctional amine monomer and a non-polar solution comprising apolyfunctional acyl halide monomer to a surface of a porous support andinterfacially polymerizing the monomers to form a polyamide layer; andii) exposing the thin film polyamide layer to nitrous acid. The methodis characterized by at least one of: conducting the interfacialpolymerization of step i) in the presence of a subject amine-reactivecompound, or applying a subject amine-reactive compound to theinterfacially polymerized polyamide layer prior to step ii), wherein thesubject amine-reactive compound is different from the polyfunctionalacyl halide monomer and the polyfunctional amine monomer and isrepresented by the following formula:

wherein:

Z is selected from: hydroxyl, alkoxy, ester, tertiary amino, andketo-amide;

Y is selected from: hydrogen, carboxylic acid, sulfonic acid or saltthereof, halogen, acyl halide, sulfonyl halide and anhydride and analkyl group having from 1 to 5 carbon atoms; and

A, A′, A″ and A′″ are independently selected from: Z, hydrogen, acylhalide, sulfonyl halide and anhydride with the proviso that at least oneof A, A′, A″ and A′″ is an acyl halide, sulfonyl halide or anhydride andthat at least one of Y, A or A″ is hydrogen.

Many additional embodiments are described.

DETAILED DESCRIPTION

The invention is not particularly limited to a specific type,construction or shape of membrane or application. For example, thepresent invention is applicable to flat sheet, tubular and hollow fiberpolyamide membranes useful in a variety of applications includingforward osmosis (FO), reverse osmosis (RO), nano filtration (NF), ultrafiltration (UF), micro filtration (MF) and pressure retarded fluidseparations. However, the invention is particularly useful in thepreparation of asymmetric membranes designed for RO and NF separations.RO membranes are relatively impermeable to virtually all dissolved saltsand typically reject more than about 95% of salts having monovalent ionssuch as sodium chloride. RO composite membranes also typically rejectmore than about 95% of inorganic molecules as well as organic moleculeswith molecular weights greater than approximately 100 AMU (Daltons). NFmembranes are more permeable than RO membranes and typically reject lessthan about 95% of salts having monovalent ions while rejecting more thanabout 50% (and often more than 90%) of salts having divalentions—depending upon the species of divalent ion. NF membranes alsotypically reject particles in the nanometer range as well as organicmolecules having molecular weights greater than approximately 200 to 500AMU.

Examples of composite polyamide membranes include FilmTec CorporationFT-30™ type membranes, i.e. a flat sheet composite membrane comprising abottom layer (back side) of a nonwoven backing web (e.g. PET scrim), amiddle layer of a porous support having a typical thickness of about25-125 μm and top layer (front side) comprising a thin film polyamidelayer having a thickness typically less than about 1 micron, e.g. from0.01 micron to 1 micron but more commonly from about 0.01 to 0.1 μm. Theporous support is typically a polymeric material having pore sizes whichare of sufficient size to permit essentially unrestricted passage ofpermeate but not large enough so as to interfere with the bridging overof a thin film polyamide layer formed thereon. For example, the poresize of the support preferably ranges from about 0.001 to 0.5 μm.Non-limiting examples of porous supports include those made of:polysulfone, polyether sulfone, polyimide, polyamide, polyetherimide,polyacrylonitrile, poly(methyl methacrylate), polyethylene,polypropylene, and various halogenated polymers such as polyvinylidenefluoride. For RO and NF applications, the porous support providesstrength but offers little resistance to fluid flow due to itsrelatively high porosity.

Due to its relative thinness, the polyamide layer is often described interms of its coating coverage or loading upon the porous support, e.g.from about 2 to 5000 mg of polyamide per square meter surface area ofporous support and more preferably from about 50 to 500 mg/m². Thepolyamide layer is preferably prepared by an interfacialpolycondensation reaction between a polyfunctional amine monomer and apolyfunctional acyl halide monomer upon the surface of the poroussupport as described in U.S. Pat. No. 4,277,344 and U.S. Pat. No.6,878,278. More specifically, the polyamide membrane layer may beprepared by interfacially polymerizing a polyfunctional amine monomerwith a polyfunctional acyl halide monomer, (wherein each term isintended to refer both to the use of a single species or multiplespecies), on at least one surface of a porous support. As used herein,the term “polyamide” refers to a polymer in which amide linkages(—C(O)NH—) occur along the molecular chain. The polyfunctional amine andpolyfunctional acyl halide monomers are most commonly applied to theporous support by way of a coating step from solution, wherein thepolyfunctional amine monomer is typically coated from an aqueous-basedor polar solution and the polyfunctional acyl halide from anorganic-based or non-polar solution. Although the coating steps need notfollow a specific order, the polyfunctional amine monomer is preferablyfirst coated on the porous support followed by the polyfunctional acylhalide. Coating can be accomplished by spraying, film coating, rolling,or through the use of a dip tank among other coating techniques. Excesssolution may be removed from the support by air knife, dryers, ovens andthe like.

The polyfunctional amine monomer comprises at least two primary aminegroups and may be aromatic (e.g., m-phenylenediamine (mPD),p-phenylenediamine, 1,3,5-triaminobenzene, 1,3,4-triaminobenzene,3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,4-diaminoanisole, andxylylenediamine) or aliphatic (e.g., ethylenediamine, propylenediamine,cyclohexanne-1,3-diamine and tris(2-aminoethyl)amine). Diamines arepreferred. One particularly preferred polyfunctional amine ism-phenylene diamine (mPD). The polyfunctional amine monomer may beapplied to the porous support as a polar solution. The polar solutionmay contain from about 0.1 to about 10 wt % and more preferably fromabout 1 to about 6 wt % polyfunctional amine monomer. In one set ofembodiments, the polar solutions includes at least 2.5 wt % (e.g. 2.5 to6 wt %) of the polyfunctional amine monomer. Once coated on the poroussupport, excess solution may be optionally removed.

The polyfunctional acyl halide monomer comprises at least two acylhalide groups and preferably no carboxylic acid functional groups andmay be coated from a non-polar solvent although the polyfunctional acylhalide may be alternatively delivered from a vapor phase (e.g., forpolyfunctional acyl halides having sufficient vapor pressure). Thepolyfunctional acyl halide is not particularly limited and aromatic oralicyclic polyfunctional acyl halides can be used along withcombinations thereof. Non-limiting examples of aromatic polyfunctionalacyl halides include: trimesic acyl chloride, terephthalic acylchloride, isophthalic acyl chloride, biphenyl dicarboxylic acylchloride, and naphthalene dicarboxylic acid dichloride. Non-limitingexamples of alicyclic polyfunctional acyl halides include: cyclopropanetri carboxylic acyl chloride, cyclobutane tetra carboxylic acylchloride, cyclopentane tri carboxylic acyl chloride, cyclopentane tetracarboxylic acyl chloride, cyclohexane tri carboxylic acyl chloride,tetrahydrofuran tetra carboxylic acyl chloride, cyclopentanedicarboxylic acyl chloride, cyclobutane dicarboxylic acyl chloride,cyclohexane dicarboxylic acyl chloride, and tetrahydrofuran dicarboxylicacyl chloride. One preferred polyfunctional acyl halide is trimesoylchloride (TMC). The polyfunctional acyl halide may be dissolved in anon-polar solvent in a range from about 0.01 to 10 wt %, preferably 0.05to 3% wt % and may be delivered as part of a continuous coatingoperation. In one set of embodiments wherein the polyfunctional aminemonomer concentration is less than 3 wt %, the polyfunctional acylhalide is less than 0.3 wt %.

Suitable non-polar solvents are those which are capable of dissolvingthe polyfunctional acyl halide and which are immiscible with water; e.g.paraffins (e.g. hexane, cyclohexane, heptane, octane, dodecane),isoparaffins (e.g. ISOPAR™ L), aromatics (e.g. Solvesso™ aromaticfluids, Varsol™ non-dearomatized fluids, benzene, alkylated benzene(e.g. toluene, xylene, trimethylbenzene isomers, diethylbenzene)) andhalogenated hydrocarbons (e.g. FREON™ series, chlorobenzene, di andtrichlorobenzene) or mixtures thereof. Preferred solvents include thosewhich pose little threat to the ozone layer and which are sufficientlysafe in terms of flashpoints and flammability to undergo routineprocessing without taking special precautions. A preferred solvent isISOPAR™ available from Exxon Chemical Company. The non-polar solutionmay include additional constituents including co-solvents, phasetransfer agents, solubilizing agents, complexing agents and acidscavengers wherein individual additives may serve multiple functions.Representative co-solvents include: benzene, toluene, xylene,mesitylene, ethyl benzene-diethylene glycol dimethyl ether,cyclohexanone, ethyl acetate, butyl Carbitol™ acetate, methyl laurateand acetone. A representative acid scavenger includes N,N-diisopropylethylamine (DIEA). The non-polar solution may also includesmall quantities of water or other polar additives but preferably at aconcentration below their solubility limit in the non-polar solution.

One or both of the polar and non-polar coating solutions mayadditionally include tri-hydrocarbyl phosphate compounds as representedby Formula I:

wherein “P” is phosphorous, “O” is oxygen and R₁, R₂ and R₃ areindependently selected from hydrogen and hydrocarbyl groups comprisingfrom 1 to 10 carbon atoms, with the proviso that no more than one of R₁,R₂ and R₃ are hydrogen. R₁, R₂ and R₃ are preferably independentlyselected from aliphatic and aromatic groups. Applicable aliphatic groupsinclude both branched and unbranched species, e.g. methyl, ethyl,propyl, isopropyl, butyl, isobutyl, pentyl, 2-pentyl, 3-pentyl.Applicable cyclic groups include cyclopentyl and cyclohexyl. Applicablearomatic groups include phenyl and naphthyl groups. Cyclo and aromaticgroups may be linked to the phosphorous atom by way of an aliphaticlinking group, e.g., methyl, ethyl, etc. The aforementioned aliphaticand aromatic groups may be unsubstituted or substituted (e.g.,substituted with methyl, ethyl, propyl, hydroxyl, amide, ether, sulfone,carbonyl, ester, cyanide, nitrile, isocyanate, urethane, beta-hydroxyester, etc); however, unsubstituted alkyl groups having from 3 to 10carbon atoms are preferred. Specific examples of tri-hydrocarbylphosphate compounds include: triethyl phosphate, tripropyl phosphate,tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triphenylphosphate, propyl biphenyl phosphate, dibutyl phenyl phosphate, butyldiethyl phosphate, dibutyl hydrogen phosphate, butyl heptyl hydrogenphosphate and butyl heptyl hexyl phosphate. The species selected shouldbe at least partially soluble in the solution from which it is coated,i.e. polar versus non-polar coating solution. Additional examples are assuch compounds are described in U.S. Pat. No. 6,878,278, U.S. Pat. No.6,723,241, U.S. Pat. No. 6,562,266 and U.S. Pat. No. 6,337,018. In onepreferred embodiment, the non-polar solution may include from 0.001 to10 wt % and more preferably from 0.01 to 1 wt % of the tri-hydrocarbylphosphate compound. In another embodiment, the non-polar solutionincludes the tri-hydrocarbyl phosphate compound in a molar(stoichiometric) ratio of 1:5 to 5:1 and more preferably 1:1 to 3:1 withthe polyfunctional acyl halide monomer.

In addition to the polyfunctional amine and acyl halide monomers,additional carboxylic acid containing monomers may be optionallyincluded in the interfacial polymerization. Representative examples aredescribed in: US2013/0287944, US2013/0287945, US2013/0287946,WO2013/048765 and WO2013/103666.

Once brought into contact with one another, the polyfunctional acylhalide and polyfunctional amine monomers react at their surfaceinterface to form a polyamide layer or film. This layer, often referredto as a polyamide “discriminating layer” or “thin film layer,” providesthe composite membrane with its principal means for separating solute(e.g. salts) from solvent (e.g. aqueous feed). The reaction time of thepolyfunctional acyl halide and the polyfunctional amine monomer may beless than one second but contact times typically range from about 1 to60 seconds. The removal of the excess solvent can be achieved by rinsingthe membrane with water and then drying at elevated temperatures, e.g.from about 40° C. to about 120° C., although air drying at ambienttemperatures may be used. However, for purposes of the presentinvention, the membrane is preferably not permitted to dry and is simplyrinsed with or dipped in water and optionally stored in a wet state.

The invention further includes the addition of a “subject”amine-reactive compound as represented below by Formula II. The subjectamine-reactive compound is different from the aforementioned monomersincluding both the polyfunctional acyl halide and polyfunctional aminemonomers. In one embodiment, the subject amine-reactive compound ispresent during the interfacial polymerization of the polyfunctionalamine and acyl halide monomers, e.g. such as by way of combination withthe polyfunctional acyl halide monomer and coated from a non-polarsolution such that the compound is incorporated throughout the resultingpolyamide layer. In an alternative embodiment, the subjectamine-reactive compound is applied to the polyamide layer after itsformation, e.g. by way of a subsequent coating step. In this alternativeembodiment, the subject amine-reactive compound preferentially reactswith residual amine groups present on the surface of the polyamidelayer. In yet another embodiment, the subject amine-reactive compound ispresent during the interfacial polymerization and is also applied to theresulting polyamide layer. The specific technique for adding or applyingthe subject amine-reactive compound is not particularly limited andincludes applying the amine-reactive compound (e.g. 10-20000 ppm) from anon-polar solution, or soaking the polyamide layer in a dip tankcontaining the subject amine-reactive compound such that the polyamidelayer becomes impregnated with the compound. After treatment with thesubject amine-reactive compound, the polyamide layer is exposed tonitrous acid.

The subject amine-reactive compound may be represented by formula II.

wherein:

Z is selected from: hydroxyl (—OH), alkoxy (e.g. wherein the alkylgroups includes from 1 to 5 carbon atoms and is preferably a methylgroup, —OCH₃), ester (e.g. —O—CO—CH₃), tertiary amino (e.g. —NRR′ whereR and R′ are alkyl groups preferably having from 1 to 5 carbon atoms),and keto-amide (e.g. —NH—COCH₃, —NH—CO—CH₂—CO—CH₃);

Y is selected from: hydrogen (—H), carboxylic acid (—COOH), sulfonicacid or salt thereof (—SO₃H), halogen (—F, —Cl, —Br, —I), acyl halide,sulfonyl halide, anhydride and an alkyl group having from 1 to 5 carbonatoms; and

A, A′, A″ and A′″ are independently selected from: Z, hydrogen and acylhalide, sulfonyl halide, anhydride with the proviso that at least one ofA, A′, A″ and A′″ is an acyl halide, sulfonyl halide or anhydride andthat at least one of Y, A or A″ is hydrogen.

In a preferred subset of embodiments: 1) Z and at least one of A′ or A′″is hydroxyl with the proviso that at least one of A or Y is hydrogen; 2)Z and at least one of A′ or A′″ is a secondary or tertiary amino withthe proviso that at least one of A or Y is hydrogen; 3) Z is selectedfrom: hydroxyl or methoxy; Y is selected from: hydrogen, halogen orcarboxylic acid; and A, A′, A″ and A′″ are independently selected from:hydrogen and acyl halide with the proviso that at least one of A, A′, A″and A′″ is an acyl halide and that at least one of A or A″ is hydrogen;4) Z is selected from hydroxyl, A′ is selected from hydroxyl and A ishydrogen provided at least one of A″, A′″ or Y is an acyl halide; and 5)Z is selected from hydroxyl, A′″ is selected from hydroxyl, Y ishydrogen provided at least one of A, A′ or A″ is an acyl halide. In eachcase, hydroxyl groups may be “protected” as an acetate ortrifluoroacetate. The “protected” groups may be subsequently removedprior to post-treatment with nitrous acid by simply washing the membranewith an aqueous solution.

Preferred species of the subject amine-reactive compound include:5-hydroxyisophthaloyl chloride, 4-hydroxyisophthaloyl chloride,3-hydroxybenzoyl chloride, 2-hydroxybenzoyl chloride, 4-hydroxybenzoylchloride, 5-hydroxybenzene-1,3-disulfonyl dichloride,5-hydroxyisobenzofuran-1,3-dione, 3-(chlorocarbonyl)-5-hydroxybenzoicacid, 3-(chlorocarbonyl)-5-hydroxybenzenesulfonic acid,3-(chlorosulfonyl)-5-hydroxybenzenesulfonic acid, 5-methoxyisophthaloylchloride, 4-methoxyisophthaloyl chloride, 3-methoxybenzoyl chloride,2-methoxybenzoyl chloride, 4-methoxybenzoyl chloride, 5-methoxybenzene-1,3-disulfonyl dichloride, 5-methoxyisobenzofuran-1,3-dione,3-(chlorocarbonyl)-5-methoxybenzoic acid,3-(chlorocarbonyl)-5-methoxybenzenesulfonic acid,3-(chlorosulfonyl)-5-methoxybenzenesulfonic acid,3,5-bis(dimethylamino)benzoyl chloride, 3-(dimethylamino)benzoylchloride, 5-(dimethylamino)isophthaloyl dichloride,3,5-bis(3-oxobutanamido)benzoyl chloride, 4-(3-oxobutanamido)benzoylchloride, 5-(chlorocarbonyl)-1,3-phenylene bis(2,2,2-trifluoroacetate)and 5-(chlorocarbonyl)-1,3-phenylene diacetate. Representative chemicalformula are as follows:

Post-Treatment of Polyamide Membrane

A variety of applicable techniques for post-treating the polyamide layerwith nitrous acid are described in U.S. Pat. No. 4,888,116 and areincorporated herein by reference. It is believed that the nitrous acidreacts with the residual primary amine groups present in the polyamidediscrimination layer to form diazonium salt groups, a portion of whichreact with the subject amine-reactive compounds, residual unreactedamines in the polyamide layer or phenols resulting hydrolysis of thediazonium salt to form azo groups, i.e. form crosslinks in the polyamidestructure. A representative reaction scheme is provided below.

In one embodiment, an aqueous solution of nitrous acid is applied to thethin film polyamide layer. Although the aqueous solution may includenitrous acid, it preferably includes reagents that form nitrous acid insitu, e.g. an alkali metal nitrite in an acid solution or nitrosylsulfuric acid. Because nitrous acid is volatile and subject todecomposition, it is preferably formed by reaction of an alkali metalnitrite in an acidic solution in contact with the polyamidediscriminating layer. Generally, if the pH of the aqueous solution isless than about 7, (preferably less than about 5), an alkali metalnitrite will react to liberate nitrous acid. Sodium nitrite reacted withhydrochloric or sulfuric acid in an aqueous solution is especiallypreferred for formation of nitrous acid. The aqueous solution mayfurther include wetting agents or surfactants. The concentration of thenitrous acid in the aqueous solution is preferably from 0.01 to 1 wt %.Generally, the nitrous acid is more soluble at 5° than at 20° C. andsomewhat higher concentrations of nitrous acid are operable at lowertemperatures. Higher concentrations are operable so long as the membraneis not deleteriously affected and the solutions can be handled safely.In general, concentrations of nitrous acid higher than about one-half(0.5) percent are not preferred because of difficulties in handlingthese solutions. Preferably, the nitrous acid is present at aconcentration of about 0.1 weight percent or less because of its limitedsolubility at atmospheric pressure. The temperature at which themembrane is contacted can vary over a wide range. Inasmuch as thenitrous acid is not particularly stable, it is generally desirable touse contact temperatures in the range from about 0° to about 30° C.,with temperatures in the range from 0° to about 20° C. being preferred.Temperatures higher than this range can increase the need forventilation or super-atmospheric pressure above the treating solution.Temperatures below the preferred range generally result in reducedreaction and diffusion rates.

One preferred application technique involves passing the aqueous nitrousacid solution over the surface of the membrane in a continuous stream.This allows the use of relatively low concentrations of nitrous acid.When the nitrous acid is depleted from the treating medium, it can bereplenished and the medium recycled to the membrane surface foradditional treatment. Batch treatments are also operable. The specifictechnique for applying aqueous nitrous acid is not particularly limitedand includes spraying, film coating, rolling, or through the use of adip tank among other application techniques. Once treated the membranemay be washed with water and stored either wet or dry prior to use.

The reaction between the nitrous acid and the primary amine groups ofthe polyamide layer occurs relatively quickly once the nitrous acid hasdiffused into the membrane. The time required for diffusion and thedesired reaction to occur will depend upon the concentration of nitrousacid, any pre-wetting of the membrane, the concentration of primaryamine groups present, the 3 dimensional structure of the membrane andthe temperature at which contact occurs. Contact times may vary from afew minutes to a few days. The optimum reaction time can be readilydetermined empirically for a particular membrane and treatment. Afterthe residual amine moieties have been converted to the diazonium salts,the pH can be raised to 6-9 and the temperature increased to 25° C. toinitiate hydrolysis of a fraction of the diazonium salts to phenols andazo-coupling between diazonium salts, phenols or the functionalizedrings originating from incorporation of the subject acid chlorides.

The thin film polyamide layer may optionally include hygroscopicpolymers upon at least a portion of its surface. Such polymers includepolymeric surfactants, polyacrylic acid, polyvinyl acetate, polyalkyleneoxide compounds, poly(oxazoline) compounds, polyacrylamides and relatedreaction products as generally described in U.S. Pat. No. 6,280,853;U.S. Pat. No. 7,815,987; U.S. Pat. No. 7,918,349 and U.S. Pat. No.7,905,361. In some embodiments, such polymers may be blended and/orreacted and may be coated or otherwise applied to the polyamide membranefrom a common solution, or applied sequentially.

Many embodiments of the invention have been described and in someinstances certain embodiments, selections, ranges, constituents, orother features have been characterized as being “preferred.”Characterizations of “preferred” features should in no way beinterpreted as deeming such features as being required, essential orcritical to the invention.

EXAMPLES Example 1

Sample membranes were prepared using a pilot scale membranemanufacturing line. Polysulfone supports were cast from 16.5 wt %solutions in dimethylformamide (DMF) and subsequently soaked in anaqueous solution of meta-phenylene diamine (mPD). The mPD was keptconstant at 3.5 wt %. The resulting support was then pulled through areaction table at constant speed while a thin, uniform layer of anon-polar coating solution was applied. The non-polar coating solutionincluded an isoparaffinic solvent (ISOPAR L) (90 vol %) and mesitylene(10 vol %), a combination of trimesoyl acid chloride (TMC), and5-hydroxyisophthaloyl chloride (OH-IPC) in different ratios. The totalacid chloride concentration was kept fixed at 0.2% w/v. Excess non-polarsolution was removed and the resulting composite membrane was passedthrough water rinse tanks and drying ovens. Sample membrane sheets were(i) stored in pH 8 deionized water until testing; or (ii) soaked forapproximately 15 minutes in a solution at 0-5° C. prepared by combining0.05% w/v NaNO₂ and 0.1 w/v % HCl and thereafter rinsed and stored in pH8 deionized water until testing. Testing was conducted with a mixture of2000 ppm NaCl solution at room temperature, pH 8 and 150 psi.

Table 1 below reports the flux and salt passage (SP) data for a seriesof membranes made with increasing concentration of OH-IPC in the organicphase. As the total acid chloride concentration was fixed in the organicphase, TMC concentration was decreased with increasing OH-IPC conc. Themembranes were post-treated and the performance data was measured.Increase in flux due to post-treatment was calculated and reported inthe Table. As illustrated by the data, the percent increase in fluximproved with increasing concentration of OH-IPC in the system. It ishypothesized that the amount of OH-IPC in the polymer provided moreactive sites for azo coupling and also influencing the distribution andconcentration of azo crosslinking leading to a different polymermorphology which enabled a higher percentage increase in flux withdiazotization as compared with the control (1).

TABLE 1 Before After Exam- TMC OH-IPC treatment treatment Flux ple % %Flux SP Flux SP increase No. w/v w/v (GFD) (%) (GFD) (%) (%) 1-1 0.2 031.4 0.58% 43.7 0.73% 39 1-2 0.17 0.03 32.0 0.67% 44.6 0.82% 39.4 1-30.14 0.06 30.9 0.67% 46.4 0.87% 50

Example 2

Sample membranes were prepared using a pilot scale membranemanufacturing line. Polysulfone supports were cast from 16.5 wt %solutions in dimethylformamide (DMF) and subsequently soaked in anaqueous solution meta-phenylene diamine (mPD). The mPD was kept constantat 4.5 wt %. The resulting support was then pulled through a reactiontable at constant speed while a thin, uniform layer of a non-polarcoating solution was applied. The non-polar coating solution included anisoparaffinic solvent (ISOPAR L) and a combination of trimesoyl acidchloride (TMC) and tributyl phosphate (1:1.1). The total acid chlorideconcentration was kept fixed at 0.2% w/v. Before the membrane wasimmersed in dip tank, it was further coated (“double coated”) withdifferent reagents. As shown in Table 2, for the first run no doublecoating was performed. Sample 2-2 was double coated with Isopar andSample 2-3 with a mixture of Isopar and mesitylene. For Samples 2-4 and2-5, the double coating solution contained 4-methoxybenzoyl chloride ina 90:10 (volume ratio) mixture of Isopar and mesitylene. For Samples 2-6and 2-7, the double coating species was 4-nitrobenzoyl chloridedissolved in 90:10 volume ratio mixture of Isopar and mesitylene.Presence of methoxy group in 4-methoxybenzoylchloride was expected toactivate the benzene ring and make it a suitable candidate for diazoniumacceptor species during azo coupling step. Whereas the nitro group in4-nitobenzoylchloride was expected to deactivate the benzene ring,making it less reactive to azo coupling reaction. Thus, while aperformance change for 4-methoxy benzoyl chloride was expected, noimprovement was expected for 4-nitro benzoyl chloride. Sample membranesheets were (i) stored in pH 6 deionized water until testing; or (ii)soaked for approximately 15 minutes in a solution at 0-5° C. prepared bycombining 0.05% w/v NaNO2 and 0.1 w/v % HCl and thereafter rinsed andstored in pH 6 deionized water until testing. Testing was conducted witha mixture of 2000 ppm NaCl solution at room temperature, pH 8 and 150psi. As summarized in Table 2 below, the percent increase in flux afterpost-treatment was a function of the concentration of 4-methoxybenzoylchloride. As compared with Sample 2-3 control), Sample 2-5 had anoticeable increase in flux. In contrast for the 4-nitrobenzoylchloride, no increase in flux was observed.

TABLE 2 Control Post treatment with (no double coating) nitrous acid (pH6) Salt Salt Ex. Double coating Flux Passage Flux Passage (%) Flux No.solution (%) (GFD) (%) (GFD) (%) increase 2-1 0 34.5 0.44% 37.6 0.56%9.0 2-2 Isopar 33 0.44% 36.7 0.50% 11.2 2-3 Isopar:mesitylene (90:10) 310.36% 34 0.40% 9.7 2-4 4-methoxybenzoylchloride 33 0.33% 37.3 0.39% 13.1(20 mMol/L) 2-5 4-methoxybenzoylchloride 32.4 0.36% 39.1 0.54% 20.7 (40mMol/L) 2-6 4-nitrobenzoylchloride 27.9 0.33% 30.7 0.40% 9.9 (20 mMol/L)2-7 4-nitrobenzoylchloride 25.3 0.28% 23.3 0.29% −8.0 (40 mMol/L)

Example 3

Membranes were prepared in a manner similar Example 2 and double coatedwith a 90:10 wt % solution of Isopar and mesitylene containing 5-hydroxyisophthaloyl chloride monomer. Unlike 4-methoxy benzoyl chloride, wherethe moiety can attach to one residual amine group during the doublecoating process, in this case 5-hydroxy isophthaloyl chloride can reactwith two adjacent pendant amine end groups making the membrane morerigid. Further rigidity would be expected after the diazotization. Asillustrated in the data of Table 3, the membranes which were doublecoated with 5-hydroxy isophthaloyl chloride showed a significantimprovement in rejection after the post treatment as compared to thoseof control samples.

TABLE 3 Control Exam- (no treatment) Post-treated % Flux % SP ple Doublecoating Flux SP Flux SP increase for std increase for std No. solution(%) (GFD) (%) (GFD) (%) post-treatment post-treatment 3-1 no 30.5 0.3738.1 0.47 25.0 25.5 3-2 Isopar:mesitylene (90:10) 31.5 0.34 39.7 0.4425.8 30.6 3-3 5-hydroxyisophthaloyl 25.2 0.35 29.3 0.31 16.1 −11.1dichloride (20 mMol/L)

The invention claimed is:
 1. A method for making a composite polyamidemembrane comprising a porous support and a polyamide layer, wherein themethod comprises the steps of: i) applying a polar solution comprising apolyfunctional amine monomer and a non-polar solution comprising apolyfunctional acyl halide monomer to a surface of a porous support andinterfacially polymerizing the monomers to form a polyamide layer; andii) exposing the thin film polyamide layer to nitrous acid; wherein themethod is characterized by at least one of: a) conducting theinterfacial polymerization of step i) in the presence of a subjectamine-reactive compound, and b) applying a subject amine-reactivecompound to the interfacially polymerized polyamide layer prior to stepii), wherein the subject amine-reactive compound is different from thepolyfunctional acyl halide and polyfunctional amine monomers and isrepresented by the following formula:

wherein: Z is selected from: hydroxyl, alkoxy, ester, tertiary amino,secondary amino and keto-amide; Y is selected from: hydrogen, carboxylicacid, sulfonic acid or salt thereof, halogen, acyl halide, sulfonylhalide and anhydride and an alkyl group having from 1 to 5 carbon atoms;and A, A′, A″ and A′″ are independently selected from: Z, hydrogen, acylhalide, sulfonyl halide and anhydride with the proviso that at least oneof A, A′, A″ and A′″ is an acyl halide, sulfonyl halide or anhydride andthat at least one of Y, A or A″ is hydrogen.
 2. The method of claim 1wherein Z and at least one of A′ or A′″ is hydroxyl with the provisothat at least one of A or Y is hydrogen.
 3. The method of claim 1wherein Z and at least one of A′ or A′″ is a secondary or tertiary aminowith the proviso that at least one of A or Y is hydrogen.
 4. The methodof claim 1 wherein: Z is selected from: hydroxyl or methoxy; Y isselected from: hydrogen, halogen or carboxylic acid; and A, A′, A″ andA′″ are independently selected from: hydrogen and acyl halide with theproviso that at least one of A, A′, A″ and A′″ is an acyl halide andthat at least one of A or A″ is hydrogen.
 5. The method of claim 1wherein: Z is selected from hydroxyl, A′ is selected from hydroxyl and Ais hydrogen provided at least one of A″, A′″ or Y is an acyl halide. 6.The method of claim 1 wherein: Z is selected from hydroxyl, A′″ isselected from hydroxyl, Y is hydrogen provided at least one of A, A′ orA″ is an acyl halide.
 7. The method of claim 1 wherein thepolyfunctional amine is a difunctional amine.
 8. The method of claim 1wherein at least one of the polar and non-polar solutions furthercomprises a tri-hydrocarbyl phosphate compound represented by followingformula:

wherein R₁, R₂ and R₃ are independently selected from hydrogen andhydrocarbyl groups comprising from 1 to 10 carbon atoms, with theproviso that no more than one of R₁, R₂ and R₃ are hydrogen.
 9. Themethod of claim 1 wherein the subject amine-reactive compound iscombined with the polyfunctional acyl halide monomer within thenon-polar solution of step i).
 10. The method of claim 1 wherein thesubject amine-reactive compound is selected from at least one of:5-hydroxyisophthaloyl chloride, 4-hydroxyisophthaloyl chloride,3-hydroxybenzoyl chloride, 2-hydroxybenzoyl chloride, 4-hydroxybenzoylchloride, 5-hydroxybenzene-1,3-disulfonyl dichloride,5-hydroxyisobenzofuran-1,3-dione, 3-(chlorocarbonyl)-5-hydroxybenzoicacid, 3-(chlorocarbonyl)-5-hydroxybenzenesulfonic acid,3-(chlorosulfonyl)-5-hydroxybenzenesulfonic acid, 5-methoxyisophthaloylchloride, 4-methoxyisophthaloyl chloride, 3-methoxybenzoyl chloride,2-methoxybenzoyl chloride, 4-methoxybenzoyl chloride,5-methoxybenzene-1,3-disulfonyl dichloride,5-methoxyisobenzofuran-1,3-dione, 3-(chlorocarbonyl)-5-methoxybenzoicacid, 3-(chlorocarbonyl)-5-methoxybenzenesulfonic acid,3-(chlorosulfonyl)-5-methoxybenzenesulfonic acid, 3,5-bis(dimethylamino)benzoyl chloride, 3-(dimethylamino)benzoyl chloride, 5-(dimethylamino)isophthaloyl dichloride, 5-(chlorocarbonyl)-1,3-phenylenebis(2,2,2 trifluoroacetate), 5-(chlorocarbonyl)-1,3-phenylene diacetate,3,5-bis(3-oxobutanamido)benzoyl chloride, and 4-(3-oxobutanamido)benzoylchloride.